Fluorescent ballast



July 18, 1950 E. E. TURNER, JR 2,515,676

FLUORESCENT BALLAST Filed Nov. 28, 1945 1 l I l Ll I 44 FIG.5

INVENTOR.

EDWIN E. TURNER JR.

Patented July 18, 1950 UNITED" STATES PATENT OFFICE FLUORESCENT BALLAST Edwin E. Turner, Jr., West Roxbury, Mass, as-

signor to Tobe Deutschmann, Canton, Mass.

Application November 28, 1945-, Serial No. 631,424

3 Claims. (Cl. 315-243) The present invention relates to ballast units for fluorescent lamplighting, and has for its purpose the. construction of a simple ballast. unit avoidingv transformers and large chokes.

In the art .of. fluorescent lighting, it is well known that considerably higher voltage is re.- quired to start the. fluorescent discharge in. the tube. than tocontinue it after ionization. in the tube. has occurred. In order to provide the higher starting voltage, it is customary to use a transformer, usually of the auto-transformer type, and in addition to this a choke or two in series with each fluorescent tube in the system. When the discharge has started and the higher voltage is no longer necessary, the auto-transformer is undesirable, but since. it is. in the starting circuit, it remains in the circuit during the running operation.

In the present invention a fluorescent ballast unit has been invented, whichwill provide the necessary higher voltage under starting conditions while under running conditions it will have substantially no efiect in the operating circuit so that efiici'ent' running operation will be obtained with unity power factor. A desired phase shift between pairs of fluorescent tubes to overcome the stroboscopic efi'ect' which tends to impair utility of" fluorescent lighting may also be provided in the present invention.

The unit of'the present invention may be made as a single element providing both the desired inductance and capacitance for operating the fluorescent light;

The present invention will'be more clearly understood' from the description and specification below when taken in connection with the drawings, in which Figure 1 shows the electrical circuit. for a fluore'scent ballast unit in accordance with the present invention.

Figure 2 shows a combination oftwo such units in which one is given a leading phase and the other a lagging phase.

Figure 3 shows partly diagrammatically the electrical circuit for the fluorescent ballast employing a single ballast.

Figure 3a shows the electrical circuit of Figure 3.

Figure 4 shows partly diagrammatically a modification of the arrangement of Figure 3.

Figure 4a shows the electrical circuit diagrammatically' of the device shown in Figure 4.

Figure 5 shows a plan view of the ballast unit according to the present invention corresponding to the forms of Figures or Figure 4, and,

2 Figure 6. shows a ectional view taken on the line 68 of Figure 5.

In the arrangement of Figure l the ballast unit comprises an inductance I and a capacity 2, inductance being connected in the line and the capacity being connected across the line between the 3 and the adjacent inductance terminal. When the lamp is not running, its resistance is practically infinite so that under these conditions the existing circuit comprises the inductance I and the capacity 2 connected across the line. This latter circuit is tuned for the operating frequency as, for instance, cycles, in which case the condition is fulfilled that which is a resonant condition for the circuit.

Other starting conditions are as follows:

Where Q-- X W L and V -VQ V is L is the inductance V0 is the voltage across the condenser. the voltage across the line. of I. C is the capacity of R1 is the resistance in the inductance. Z is in the input impedance. W=21r times the frequency.

If in the above arrangement, R1 is small compared to the inductive or capacitance reactance, X1 or Xe respectively, then the voltage developed across the capacity which is the same as the voltage across the lamp may be extremely high since this voltage is equal to the line voltage times 1 It will be evident therefore, that starting of the lamp Will be readily accomplished.

Under running conditions, since the inductive reactance and the capacitance reactance are equal and opposite they will cancel themselves out, one providing a leading phase and the other providing a lagging phase. The only additional consumption of power beside that used in the lamp will be that of the loss in the inductance, namely, the loss due to the quantity R1. The phase shift between the input voltage and the voltage across the lamp to the inductance in the line will be somewhat less than lagging.

In the arrangement of Figure l, the usual fluorescent lamp arrangement is shown consisting of the two heaters 4 and 5, a heater switch 5 which opens after a short time interval and the capacitor 1 across the switch element 5.

If it is desired to use a circuit of twolamps, one

circuit may be provided with a phase lag of somewhat less than 90, and the other circuit with a phase lead of somewhat less than 90. This is illustrated in Figure 2 where the lamp 8 is arranged in the same way as the circuit of Figure 1 with a series inductance 9 and a capacity shunt I while the lamp II is provided with a series capacity l2 and aninductive shunt l3. The lamp 8 lags the line voltage in operation because of the inductance 9 while the lamp ll leads the line voltage because of the capacity 12. The two lamps, because of their characteristics, will, therefore, have a phase difference of approximately 90, while the circuits will have a phase difference of somewhat less than 180, which means that each will light alternately twice in a complete cycle. The resistive reactance of the lamps when lighting will pull the phase together to approximately 90. the occurrence of the discharge will be at the rate of 240 times per second, which by proper design can be spaced substantially uniformly from each other. As a result of this, the stroboscopic efiect will be substantially eliminated.

The unit providing the capacity and inductance is illustrated somewhat diagrammatically in Figures 3 and 3a. In these figures two conductive foils or sheets I4 and [5 are wound about a central core 16 permeable to magnetic flux. The conductive foils l4 and !5 are separated by suitable insulating sheets IT. The sheets [4 and [5 provide a capacity between one another while the windings themselves provide the inductance. The circuit may be traced as follows: Commencing from one supply line It, current will pass through the winding I4 in a. clock-wise direction from the initial terminal a to the end terminal 0. Current will then fiow through the lead is to the lamp 20, out of the lamp 29 from the lead 2i to the terminal point at which is the beginning of the second winding I5, through the second winding IE to the terminal b and out through the terminal along the supply line 22.

The equivalentc'ircuit is set up in Figure 3a where the terminal points a, b, c and d designate the same terminals as in Figure 3 and the lamp the same lamp as in Figure 3. The inductance 23 corresponds to the winding I 4 whil the inductance 24 corresponds to the winding l5. Winding 23 and 24 link the same flux and have very close coupling between them.

In the arrangement of Figures 3 and 3a, it will be seen that current flows through both windings I4 and It in the same direction. The effective capacity between the windin l4 and I5 is, of course distributed all the way between both windings. It will be noted however, that these distributed capacities run criss-cross from the beginning of one inductance to the .end'of the other inductance, looking into the unit from the line side. These distributed capacities are represented by lumped capacity units in th elements 25 and 25. For resonant conditions the voltage on starting across the tube 20 will be equal to Q X the line voltage, as in the equa- V tions given above. This is of course, forresonance in the circuits providing the inductance At 60 cycles, therefore,

'4 are all tied together. A single capacitance is, therefore, set up distributing from the windings 30 to what may be considered a single element 3| connected to the opposite side of the line, as for instance, the line 32. In Figure 4, therefore, the input side is represented by the two lines 32 and 33 while the output to the lamp is represented by the lines 32 and 34. Between the line 33 and 34 is the inductance winding 30 and across the line is the distributed capacity between the winding 30 and the shorted winding 3|. The circuit of Figure 4, it will be seen, is therefore substantially the equivalent of the circuit of Figure 1 with the exception that the capacity in Figure 4a is distributed over the whole winding. The same equations apply to Figure 4a as set forth in Figure 1.

In Figures 5 and 6 there is shown an element for providing the inductance and capacitances necessary for operation of the fluorescent lamps as diagrammatically represented in the other figures. Here the roll 40 may be formed of windings of pairs of conductive foils 4| and 42 separated by insulating and dielectric elements 43. These windings may be made on a core 44 with an air'gap 44' to increase the magnetic reluctance and provide partial saturation to limit open load current. Under these conditions the inductance is decreased with respect to a tuned condition or in efiect the circuit is somewhat detuned. The core 44 is of material permeable to magnetic flux. If desired an open core might be used. However Figure 5 shows a closed core, the path being closed by the outside element 45. The conductive foil may be of any suitable metallic foil, as for instance, aluminum, copper or some alloy. The electrical circuit may be connected either according to the means set forth in Figures 3, 3a or 4. The distributed capacity may be tuned with inductance to resonance for the figuring of the supply source. Only one element therefore is needed, the power factor at the line will be zero and loss and heating will be kept to a minimum.

Having now described'my invention, I claim:

1. A lighting circuit including a supply line, a fluorescent lamp and a fluorescent ballast unit comprising two windings of conductive foil elements having separator sheets formed as a dielectric insulator, one winding having turns connected together at one end of the winding roll and connected to one side of the supply line, the other winding being connected in series with the line, said fluorescent lamp being connected across the line after the series and shunt ballast connections.

2. A lighting circuit including a supply line and a fluorescent ballast unit comprising two windings of conductive foil elements having separator sheets formed as a dielectric insulator,

permeable to magnetic flux around whichthe windings are placed.

3. A lighting circuit including a supply line and a fluorescent ballast unitcomprising two windings of conductive foil elements having separator sheets formed as a dielectric insulator, one winding having turns connected together at one end of the winding roll and connected to one side of the supply line, the other winding being connected in series with the line, a fluorescent lamp being connected across the line after the series and shunt ballast connections, said unit being tuned to resonance at the frequency of the supply current.

EDWIN E. TURNER, JR.

REFERENCES CITED The following references are of record in the file of this patent:

Number 6 UNITED STATES PATENTS Name Date Williams Jan. 3, 1899 Schiessler Nov. 3, 1914 OLeary July 3, 1923 Soundy Aug. 15, 1933 Culver Oct. 9, 1934 Mutsaers Dec. 18, 1934 Osborne Dec. 24, 1935 McCarthy Mar. 26, 1940 

